Effect of artificial shading on growth and competitiveness of Alternanthera philoxeroides (alligator weed)

Abstract

Terrestrial Alternanthera philoxeroides is difficult to control with current tools. Shading as a control tool depends on the relative shade tolerances of the target weed and co-occurring species. This study examined A. philoxeroides’ shade tolerance with inter-specific competition from pasture species. In glasshouse conditions, shade and competition reduced A. philoxeroides growth but did not cause senescence. Grasses senesced in response to shade. In the field, competing species’ biomass reduced by over 90% in shade. A. philoxeroides biomass was unaffected by shade, contrasting with glasshouse results and resulting in increased dominance in shade. Connection to unshaded ramets in the glasshouse reduced some, but not all, of the differences between shaded and unshaded plants. Thus, resource sharing likely facilitated A. philoxeroides growth in the field, but may have been less influential than release from inter-specific competition. This research suggests shading may have limited use for controlling A. philoxeroides unless shade-tolerant inter-specific competition is provided.

Keywords:

• alligator weed
• Alternanthera philoxeroides
• competition
• invasive species
• light
• resource sharing
• shade
• weed control

Acknowledgements

The authors would like to acknowledge funding from the University of Auckland, Landcare Research and the Co-operative Research Center for Australian Weed Management. Comments from Peter Williams and Adrian Walcroft improved this manuscript.